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Layered transition metal chalcogenides (Zr,Hf)GeTe4 were screened from the AtomWork database as potential pressure-induced superconductors by having a narrow bandgap and high density of states near...

The processing of promising magnetocaloric materials into spheres is one of the important issues on developing high-performance magnetic refrigeration systems. In the present study, we achieved in producing spherical particles of a giant magnetocaloric compound HoB2 by a crucible-free gas atomization process, despite its high melting point of 2350 C. The particle size distribution ranges from 100 to 710 micrometers centered at 212-355 micrometers with the highest yield of 14-20wt% of total melted electrode, which is suitable for magnetic refrigeration systems. The majority of the resulting particles are mostly spherical with no contamination during the processing, while unique microstructures are observed on the surface and inside. These spherical particles exhibit sharp magnetic transitions and huge magnetic entropy change of 0.34 J cm^{-3} K^{-1} for a magnetic field change of 5 T at 15.5 K. The high sphericality and the high magnetocaloric performance suggest that the HoB2 gas-atomized particles have good potential as magnetic refrigerants for use in magnetic refrigerators for hydrogen liquefaction., Comment: 6pages(double column), 6 figures

Recently, a massive magnetocaloric effect near the liquefaction temperature of hydrogen has been reported in the ferromagnetic material HoB$_{2}$. Here we investigate the effects of Dy substitution in the magnetocaloric properties of Ho$_{1-x}$Dy$_{x}$B$_{2}$ alloys ($\textit{x}$ = 0, 0.3, 0.5, 0.7, 1.0). We find that the Curie temperature ($\textit{T}$$_{C}$) gradually increases upon Dy substitution, while the magnitude of the magnetic entropy change |$\Delta \textit{S}_{M}$| at $\textit{T}$ = $\textit{T}_{C}$ decreases from 0.35 to 0.15 J cm$^{-3}$ K$^{-1}$ for a field change of 5 T. Due to the presence of two magnetic transitions in these alloys, despite the change in the peak magnitude of |$\Delta \textit{S}_{M}$|, the refrigerant capacity ($\textit{RC}$) and refrigerant cooling power ($\textit{RCP}$) remains almost constant in all doping range, which as large as 5.5 J cm$^{-3}$ and 7.0 J cm$^{-3}$ for a field change of 5 T. These results imply that this series of alloys could be an exciting candidate for magnetic refrigeration in the temperature range between 10-50 K., Comment: 19 pages, 5 figures, 2 tables

Data-driven exploration for pressure-induced superconductors was performed based on the high-throughput first-principles screening of electronic band structures. In the screening conditions, we foc...

Magnetic refrigeration exploits the magnetocaloric effect which is the entropy change upon application and removal of magnetic fields in materials, providing an alternate path for refrigeration other than the conventional gas cycles. While intensive research has uncovered a vast number of magnetic materials which exhibits large magnetocaloric effect, these properties for a large number of compounds still remain unknown. To explore new functional materials in this unknown space, machine learning is used as a guide for selecting materials which could exhibit large magnetocaloric effect. By this approach, HoB$_{2}$ is singled out, synthesized and its magnetocaloric properties are evaluated, leading to the experimental discovery of gigantic magnetic entropy change 40.1 J kg$^{-1}$ K$^{-1}$ (0.35 J cm$^{-3}$ K$^{-1}$) for a field change of 5 T in the vicinity of a ferromagnetic second-order phase transition with a Curie temperature of 15 K. This is the highest value reported so far, to our knowledge, near the hydrogen liquefaction temperature thus it is a highly suitable material for hydrogen liquefaction and low temperature magnetic cooling applications., 12 pages including 3 figures and 1 table + 11 pages of supplementary information. Published version available at: https://rdcu.be/b36ep

Candidate compounds for new thermoelectric and superconducting materials, which have narrow band gap and flat bands near band edges, were exhaustively searched by the high-throughput first-principles calculation from an inorganic materials database named AtomWork. We focused on PbBi2Te4 which has the similar electronic band structure and the same crystal structure with those of a pressure-induced superconductor SnBi2Se4 explored by the same data-driven approach. The PbBi2Te4 was successfully synthesized as single crystals using a melt and slow cooling method. The core level X-ray photoelectron spectroscopy analysis revealed Pb2+, Bi3+ and Te2- valence states in PbBi2Te4. The thermoelectric properties of the PbBi2Te4 sample were measured at ambient pressure and the electrical resistance was also evaluated under high pressure using a diamond anvil cell with boron-doped diamond electrodes. The resistance decreased with increasing of the pressure, and pressure-induced superconducting transitions were discovered at 2.5 K under 10 GPa. The maximum superconducting transition temperature increased up to 8.4 K at 21.7 GPa. The data-driven approach shows promising power to accelerate the discovery of new thermoelectric and superconducting materials.

The crystal structure of type I clathrate Ba8Al16Ge30 prepared by arc melting in argon atmosphere has been studied by using a neutron powder diffractometer from 10 to 900 K. We found that the site preferences in the host structure were relevant to the guest atom features, which agrees with a previous report. Data were analyzed using two models for the Ba atom position in the larger cage (Ba2): an on-center 6d-site model and an off-center 24k-site one. The Maximum Entropy Method (MEM) results agree well with the 24k model and the shape of the nuclear density distribution of Ba2 atom evolves with increasing temperature.

It is now well established that the microstructure of Fe-based chalcogenide K x Fe2−ySe2 consists of, at least, a minor (~15 percent), nano-sized, superconducting K s Fe2Se2 phase and a major (~85 percent) insulating antiferromagnetic K2Fe4Se5 matrix. Other intercalated A1−xFe2−ySe2 (A = Li, Na, Ba, Sr, Ca, Yb, Eu, ammonia, amide, pyridine, ethylenediamine etc.) manifest a similar microstructure. On subjecting each of these systems to a varying control parameter (e.g. heat treatment, concentration x,y, or pressure p), one obtains an exotic normal-state and superconducting phase diagram. With the objective of rationalizing the properties of such a diagram, we envisage a system consisting of nanosized superconducting granules which are embedded within an insulating continuum. Then, based on the standard granular superconductor model, an induced variation in size, distribution, separation and Fe-content of the superconducting granules can be expressed in terms of model parameters (e.g. tunneling conductance, g, Coulomb charging energy, E c , superconducting gap of single granule, Δ, and Josephson energy J = πΔg/2). We show, with illustration from experiments, that this granular scenario explains satisfactorily the evolution of normal-state and superconducting properties (best visualized on a $${\boldsymbol{g}}{\boldsymbol{-}}\frac{{{\boldsymbol{E}}}_{{\boldsymbol{c}}}}{{\boldsymbol{\Delta }}}{\boldsymbol{-}}{\boldsymbol{T}}$$ g − E c Δ − T phase diagram) of A x Fe2−ySe2 when any of x, y, p, or heat treatment is varied.

DyNi $$_{2}$$ B $$_{2}$$ C superconducts at $$T_{c} \approx 6\,{\text{K}}$$ and orders antiferromagnetically at $$T_{N}\approx 10\,{\text{K}}.$$ Its non-superconducting isomorph DyCo $$_{2}$$ B $$_{2}$$ C is a ferromagnet with $$T_{C}\approx 6\,{\text{K}}.$$ With the aim of mapping out the magnetic properties, in particular magnetic structures, of their solid solutions, we synthesized $$^{11}$$ B-enriched Dy(Co $$_{x}$$ Ni $$_{1-x}$$ ) $$_{2}$$ B $$_{2}$$ C ( $$x=0.2,0.4,0.6,0.8$$ ). We investigated the evolution of their magnetic, thermal and transport properties by means of the magnetization, resistivity, specific heat and neutron diffraction techniques. Their crystal structures were confirmed to be ThCr $$_{2}$$ -Si $$_{2}$$ -type tetragonal (I4/mmm) phase. The magnetic structure was found to be antiferromagnetic with k0.2 = (0, 0, 1) for x = 0.2; helicoidal with k $$_{0.4}$$ = (0, 0, 0.49) and k $$_{0.6}$$ = (0, 0, 0.46) for, respectively, x = 0.4 and 0.6 and ferromagnetic with k $$_{0.8}$$ = (0, 0, 0) for x = 0.8. We discuss the evolution of such magnetic modes assuming a scenario of an idealized one-dimensional chain of transverse magnetic moments.

For many years, cerium-aluminum systems have been extensively studied because of their unusual magnetic behavior. As the atomic radii of cerium and aluminum differ greatly from each other, a solid solution is not obtained because of the Hume-Rothery rule. Therefore, intermetallic compounds are usually studied, and structural stability is crucial for further discussion of their physical properties. The present article reports on high-energy ball milling of the intermetallic compound Ce3Al at room temperature. It has been found that non-equilibrium supersaturated Ce solid solution was formed during the milling. The solubility of aluminum was estimated as 5 to 13 at. pct from the peak shifts of the X-ray diffraction pattern. The structural changes in the initial stages of the milling were also studied.

We have developed an approach to control the carrier density in various material under high pressure by the combination of an electric double layer transistor (EDLT) with a diamond anvil cell (DAC). In this study, this EDLT-DAC was applied to a Bi thin film, and here we report the field-effect under high pressure in the material. Our EDLT-DAC is a promising device for exploring unknown physical phenomena such as high transition-temperature superconductivity (HTS)., 10 pages, 4 figures

Physical review / B 101(2), 020508 (2020). doi:10.1103/PhysRevB.101.020508, The coexistence of phases, characterized by different electronic degrees of freedom, commonly occurs in layered superconductors. Among them, alkaline intercalated chalcogenides are model systems showing the microscale coexistence of paramagnetic (PAR) and antiferromagnetic (AFM) phases, however, the temporal behavior of different phases is still unknown. Here, we report a visualization of the atomic motion in the granular phase of KxFe2−ySe2 using x-ray photon correlation spectroscopy. Unlike the PAR phase, the AFM texture reveals an intermittent dynamics with avalanches as in martensites. When cooled down across the superconducting transition temperature Tc, the AFM phase goes through an anomalous slowing behavior, suggesting a direct relationship between the atomic motions in the AFM phase and the superconductivity. In addition to providing compelling evidence of avalanchelike dynamics in a layered superconductor, the results provide a basis for different theoretical models to describe the quantum states in inhomogeneous solids., Published by Inst., Woodbury, NY

We report the fabrication of ErAl2 magnetocaloric wires by a powder-in-tube method (PIT) and the evaluation of magnetic entropy change through magnetization measurements. The magnetic entropy change of ErAl2 PIT wires exhibits similar behavior to the bulk counterpart, while its magnitude is reduced by the decrease in the volume fraction of ErAl2 due to the surrounding non-magnetic sheaths. We find that another effect reduces the magnetic entropy change of the ErAl2 PIT wires around the Curie temperature, and discuss its possible origin in terms of a correlation between magnetic properties of ErAl2 and mechanical properties of sheath material., Comment: This is the version of the article before peer review or editing, as submitted by an author to {insert name of Journal}. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at {https://dx.doi.org/10.1088/1361-6463/ab5c71}

We study the effects of the Al substitution by Ga on the crystal structures of type I clathrate Ba 8 Al 16-x Ga x Ge 30 (x = 2, 4, 6, and 8) by neutron powder diffraction. The diffraction data were refined using two models for Ba guest atom position in the oversized cage (Ba2): on center (6d site) and off-center (24k site) model. We also carried out the Maximum Entropy Method (MEM) analysis. The 24k model is in a good agreement with the Maximum Entropy Method (MEM) results. The evolution of nuclear density distribution with increasing temperature of Ba 8 Al 8 Ga 8 Ge 30 was revealed by MEM analysis.

A direct patterning technique of gallium-irradiated superconducting silicon has been established by a focused gallium-ion beam without any mask-based lithography process. The electrical transport measurements for line- and square-shaped patterns of gallium-irradiated silicon were carried out under self-field and magnetic field up to 7 T. Sharp superconducting transitions were observed in both patterns at a temperature of 7 K. The line pattern exhibited a signature of higher onset temperature at around 12 K. A critical dose amount to obtain the superconducting gallium-irradiated silicon was investigated by the fabrication of various samples with different doses. This technique can be used as a simple fabrication method for a superconducting device.

Layered ternary transition-metal chalcogenides have been focused as a vein of exploration for superconductors. In this study, TiGeTe6 single crystals were synthesized and characterized by structural and valence state analyses and electrical transport measurements. The transport properties were measured under various pressures up to 71 GPa. The activation energy gets smaller as the applied pressure increases, and a signature of a pressure-induced metallization was observed under around 8.4 GPa. Under 13 GPa, pressure-induced superconductivity was discovered in this compound for the first time, with successive drops at 3 K and 6 K in the resistance, indicating the presence of multiple superconducting transitions. The superconducting transition temperature kept increasing as we further applied the pressure to the TiGeTe6 single crystal in the performed pressure range, reaching as high as 8.1 K under 71 GPa.

A method to directly deposit boron-doped amorphous carbon films via focused ion beam-assisted chemical vapor deposition is reported. The presence of boron in the deposited films was verified by X-ray photoelectron spectroscopy. Raman spectroscopy analysis confirmed the amorphousity of the films. The as-deposited films exhibited typical semiconducting behavior from electrical resistance versus temperature measurements. The presented fabrication technique is a one step process for the simultaneous deposition, boron-doping, and patterning of the films, and hence may offer an effective way to directly fabricate boron-doped amorphous carbon-based devices without the need for templates, which is highly advantageous for applications.

To optimize the giant magnetocaloric properties of HoB2, we synthesized and characterized the magnetocaloric properties of Ho1-xGdxB2 (0.1 ≤ x ≤ 0.4) alloys. We found out that Gd enters stoichiometrically and randomly into the Ho site, leading to a Vegard-type structural change. The addition of spherical S7/2 Gd3+ moments prompts an enhancement in Curie temperature from 15 K to 30 K (at x = 0.4), a reduction in peak value of the magnetic entropy change, from 0.35 (40.1) to 0.17 (20.2) J cm−3 K−1 (J kg−1 K−1), and a broadening of the magnetic entropy change curves. The overall influence is a relatively high refrigerant capacity and relative cooling power, peaking at 6.07 (711) and 7.68 (899) J cm−3 (J kg−1) for x = 0.2, and an extension of the thermal working range to higher temperatures. Unlike Ho1−xDyxB2 alloys, the Gd substituted samples show no magnetic hysteresis. Furthermore, scaling analysis of the entropy curves suggests a second-order phase transition for the ferromagnetic transition in these alloys. Thus, Ho1-xGdxB2 alloys are potential candidates for cryogenic refrigeration applications.

Using a combination of theoretical (first-principles total-energy and electronic structure calculations) as well as experimental (structural, thermodynamics) techniques, we systematically investigated the influence of B incorporation on the structural, electronic and thermodynamic properties of a series of technologically-important B-containing AlNi matrix. Special attention was paid to calculating the energy cost of placing B at various sites within the cubic unit cell. The most energetically favorable defects were identified to be, depending on initial stoichiometry, substitutional B at Al site (B Al ), Ni vacancy ( V Ni ), or Ni antisite (Ni Al ). We show that the induced variation in the lattice parameters can be correlated with the type and concentration of the involved defects: e.g. the surge of V Ni defects leads to a stronger lattice-parameter reduction, that of Ni Al ones to a relatively weaker reduction while that of B Al defects to a much weaker influence. Both electronic band structure calculations as well as thermodynamics measurements indicate that the 3 d bands of Ni are fully occupied and magnetically unpolarized and that the resulting N ( E F ) is very small: all studied compounds are normal conductors with no trace of superconductivity or magnetic polarization.

Cuprate superconductor Bi2Sr2CaCu2O8+δ (BSCCO) has been a promising candidate of a coherent, continuous, and compact THz light source owing to its intrinsic Josephson junction (IJJ) inside the crystal structure. In this paper, we utilized BSCCO cross-whisker (CW) junctions to produce THz emitter device using the whisker crystals which can be easily obtained compared with single crystals. As a result, we have successfully observed the emission from the CW IJJ at the frequency of ∼0.7 THz, which is the first observation of a THz emission from whiskers to our knowledge. Our findings would enlarge the applicability of BSCCO superconductors for compact THz emission sources.

We report the adiabatic temperature change in ErAl2 magnetocaloric wires fabricated by a powder-in-tube (PIT) process. The adiabatic temperature change of the PIT wires is found to be determined by not only the volume fraction of ErAl2 core but also the magnitude relationship between the specific heat of the ErAl2 core and the metal sheath. We propose a quantitative analysis method for calculating the temperature and core volume fraction dependence of adiabatic temperature change in the PIT wire, whose formula is applicable to also various magnetocaloric composites, useful to estimate the magnetocaloric response prior to fabrication., Comment: 14 pages, 5 figures

A diamond anvil cell (DAC) has become an effective tool for investigating physical phenomena that occur at extremely high pressure, such as high-transition temperature superconductivity. Electrical transport measurements, which are used to characterize one of the most important properties of superconducting materials, are difficult to perform using conventional DACs. The available sample space in conventional DACs is very small and there is an added risk of electrode deformation under extreme operating conditions. To overcome these limitations, we herein report the fabrication of a boron-doped diamond microelectrode and undoped diamond insulation on a beveled culet surface of a diamond anvil. Using the newly developed DAC, we have performed in-situ electrical transport measurements on sulfur hydride H2S, which is a well-known precursor of the pressure-induced, high-transition temperature superconducting sulfur hydride, H3S. These measurements conducted under high pressures up to 192 GPa, indicated the presence of a multi-step superconducting transition, which we have attributed to elemental sulfur and possibly HS2.

We have developed the rapid growth method for HgBa2Ca2Cu3O8+δ (Hg-1223) by using a sealed quartz tube technique with a small amount of cesium chloride (CsCl). Our results suggested that a small amount of CsCl works as a flux during the crystal growth of Hg-1223. The developed method achieved the growth of the Hg-1223 single crystal pieces in 4 h. Furthermore, the grown single crystals showed high purity. The developed method is useful for application purposes such as high transition-temperature (T c) superconducting cable.

Tin sulfide (SnS) single crystals were synthesized using a melt and slow-cooling method. The obtained crystals were characterized by x-ray diffraction, energy-dispersive spectrometry, and by x-ray photoelectron spectroscopy. Electrical transport properties of SnS were investigated under high pressure using a diamond anvil cell with boron-doped metallic diamond electrodes and an undoped diamond insulating layer. We successfully observed an insulator to metal transition between 8.1 and 12.5 GPa and pressure-induced superconductivity with a transition temperature (${T}_{c}$) of 5.8 K under 47.8 GPa as predicted by theoretical calculations. Comparing with the pressure-induced superconductivity in related SnSe compound, a possible ${T}_{c}$ enhancement in SnS by an increase of density of states at the Fermi level is expected.

We have successfully synthesized the c-axis oriented YBa2Cu4O8 (Y-124) film on a SrTiO3 (1 0 0) substrate via a coprecipitation and a dip-coating method. The precipitations including Y, Ba and Cu ions were obtained using their metal nitrates solution and the aqueous solution of sodium hydroxide and oxalic acid. Superconducting transition of the synthesized film was observed at 64-70 K corresponding to bulk Y-124 in the magnetization and resistance measurement. The developed method is suitable to synthesize superconducting Y-124 films for technological applications., Comment: 7 pages, 6 figures

Transport properties of Ce$_{0.85}$F0.15SbS$_{2}$ and undoped CeOSbS$_{2}$ under high pressure were investigated experimentally and theoretically. Electrical resistivity measurements of the Ce$_{0.85}$F0.15SbS$_{2}$ single crystals were performed under various high pressures using a diamond anvil cell with boron-doped diamond electrodes. The samples showed the insulator to metal transition by applying high pressure up to 30-40 GPa. On the other hand, the undoped CeOSbS$_{2}$ showed almost same transport property with the F-doped sample under high pressure. The valence state analysis using X-ray photoelectron spectroscopy revealed a simple valence state of Ce3+ in Ce$_{0.85}$F0.15SbS$_{2}$ and mixed valence state between Ce3+ and Ce4+ in undoped CeOSbS$_{2}$. The valence fluctuation in Ce carried out the comparable transport nature in the both samples. A band calculation suggests that the undoped CeOSbS$_{2}$ could be metallic under high pressure of 30 GPa in accordance with the experimental results. A superior thermoelectric property of power factor in CeOSbS$_{2}$ was estimated under high pressure around 20 GPa in comparison with that of ambient pressure.

The ionic-liquid-gating technique can be applied to the search for novel physical phenomena at low temperatures because of its wide controllability of the charge carrier density. Ionic-liquid gated field-effect transistors are often fragile upon cooling, however, because of the large difference between the thermal expansion coefficients of frozen ionic liquids and solid target materials. In this paper, we provide a practical technique for setting up ionic-liquid-gated field-effect transistors for low-temperature measurements. It allows stable measurements and reduces the electronic inhomogeneity by reducing the shear strain generated in frozen ionic liquid., 5 pages, 6 figures

The magnetic phase diagram of the quaternary borocarbide ${\mathrm{TbNi}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ is investigated by direct means and by studying magnetically induced modifications of the crystal structure. Detailed superconducting quantum interference device measurements reveal a complex phase diagram with five distinct magnetic phases. The phase boundaries are mapped out comprehensively. Synchrotron hard x-ray measurements in applied magnetic fields are employed to probe the magnetoelastic distortions throughout the phase diagram. The determination of the wave vectors of these field-induced lattice deformations suggests a range of commensurate spin-slip-type magnetic structures at low temperatures with wave vectors of the form $(q,0,0)$ with $q=6/11$ and $5/9$. The proposed magnetic structures yield values of magnetization well in-line with observations. The scattering intensity due to the magnetoelastic deformations exhibits a drastic jump at the phase boundary at 1.3 T and low temperatures.

Diamond anvil cells using boron-doped metallic diamond electrodes covered with undoped diamond insulating layers have been developed for electrical transport measurements under high pressure. These designed diamonds were grown on a bottom diamond anvil via a nanofabrication process combining microwave plasma-assisted chemical vapor deposition and electron beam lithography. The resistance measurements of a high-quality FeSe superconducting single crystal under high pressure were successfully demonstrated by just putting the sample and gasket on the bottom diamond anvil directly. The superconducting transition temperature of the FeSe single crystal was increased to up to 43 K by applying uniaxial-like pressure.

We introduce a novel nanofabrication technique to directly deposit catalyst pads for the chemical vapor deposition synthesis of single-walled carbon nanotubes (SWCNTs) at any desired position on a substrate by Gallium focused ion beam (FIB) induced deposition of silicon oxide thin films from the metalorganic Tetraethyl orthosilicate (TEOS) precursor. A high resolution in the positioning of the SWCNTs is naturally achieved as the imaging and deposition by FIB are conducted concurrently in situ at the same selected point on the substrate. This technique has substantial advantages over the current state-of-the-art methods that are based on complex and multistep lithography processes.

Single crystals of Nd-substituted LuBa$_2$Cu$_4$O$_8$ were successfully grown by the KOH flux method. The single phase of Lu$_{1-x}$Nd$_x$Ba$_2$Cu$_4$O$_8$ [(Lu,Nd)124] formed at $x = 0.2$. The compound crystallized as orthorhombic Ammm structure with lattice constants of a = 3.835(3) {\AA}, b = 3.879(2) {\AA} and c = 27.195(6) {\AA}. Single crystal structural analysis demonstrated that the Nd ion partially occupied the Lu site. The (Lu,Nd)124 exhibited the superconducting transition at ~75 K in the magnetic susceptibility and resistivity. The $T_c$ and the c-axis of the (Lu,Nd)124 corresponded to Tm124. These results indicate that RE124 equivalent to the one composed of single RE element is obtained by combination of two RE elements., Comment: 12 pages, 5 figures

Candidates for new thermoelectric and superconducting materials, which have narrow band gap and flat bands near band edges, were searched by the high-throughput first-principles calculation from an inorganic materials database. The synthesized SnBi$_2$Se$_4$ among the target compounds showed a narrow band gap of 354 meV, and a thermal conductivity of 1 W/Km at ambient pressure. The sample SnBi$_2$Se$_4$ showed a metal-insulator transition at 11.1 GPa, as predicted by a theoretical estimation. Furthermore, the two pressure-induced superconducting transitions were discovered at under 20.2 GPa and 47.3 GPa. The data-driven search is a promising approach to discover new functional materials.

We report the pressure effect in Bi2Sr2Ca2Cu3O10+{\delta} (Bi-2223) single crystal with a small amount of intergrowth of Bi2Sr2CaCu2O8+{\delta} (Bi-2212). Their superconducting transition temperatures Tcs showed a domelike shape as a function of pressure, which showed a good agreement with the general relation between the carrier concentration and Tc. Our experimental results indicate that high pressure can induce effective carrier doping into the multilayered high-Tc cuprate superconductor, Comment: 8 pages including 5 figures

Sulfur-doped SnSe single crystal was successfully synthesized using a melt and slow-cooling method. The chemical composition and valence state of the obtained sample were analyzed by X-ray photoelectron spectroscopy. The pressure range of a diamond anvil cell with boron-doped diamond electrodes was upgraded to 104 GPa using nano-polycrystalline diamond anvil to investigate a pressure effect for the sample. Electrical resistivity measurements of sulfur-doped SnSe single crystal showed the insulator-metal-superconductor transition by applying high pressure up to 75.9 GPa.

Superconducting FeSe films were electrochemically deposited on rolling-assisted biaxially textured substrate (RABiTS) tape. We observed zero resistivity in the as-electrodeposited FeSe film prepared on the RABiTS when the appropriate voltage was applied while it was dipped into the solution. When the RABiTS tape was dipped in the solution without applying voltage, a thin Se film was deposited on the substrate. The compositional ratio of the FeSe film got closer to the stoichiometric ratio with decreasing the dipping time before applying voltage.

Here we firstly report the pressure-induced superconductivity in phase change materials SnSb2Te4. Single crystals of SnSb2Te4 were grown using a conventional melting-down method. The resistance under pressure was measured using an originally designed diamond anvil cell with boron-doped diamond electrodes. The temperature dependence of the resistance under different pressures has been measured up to 32.6 GPa. The superconducting transition of SnSb2Te4 appeared at 2.1 K ([Formula: see text]) under 8.1 GPa, which was further increased with applied pressure to a maximum onset transition temperature 7.4 K under 32.6 GPa.

We evaluated the influence of Co substitution on the magnetic structure of Ho(CoxNi1−x)2B2C (x=0.2, 0.4, 0.6, 0.8) using neutron diffraction, magnetization and specific heat studies. Different modes are stabilized: an AFM k → x = 0.2 = ( 0 , 0 , 1 ) mode for x=0.2, a spiral k → x = 0.4 = ( 0 , 0 , 0.49 ) mode for x=0.4, a spiral k → x = 0.6 = ( 0 , 0 , 0.26 ) mode for x=0.6, and a FM k → x = 0.8 = ( 0 , 0 , 0 ) mode for x=0.8. Recalling that for x=0.0, k → x = 0 = ( 0 , 0 , 1 ) while for x=1.0, k → x = 1.0 = ( 0 , 0 , 0 ) , then all these magnetic structures can be visualized as a variation in the stacking sequence, along the z-axis, of the intra-planar FM-coupled Ho sheets as such Co substitution controls the z-component of the k → x = ( 0 , 0 , u x ) vector where u x = 0 , 0.26 , 0.49 , or 1. We discuss this inference and the observation that in spite of such a diversity of magnetic structures, the critical temperatures and the saturated moments are only weakly influenced by substitution.

We report conductivity measurements for mackinawite at atmospheric pressure and up to values of 1.64 GPa. As far as the authors are aware, this is the first low temperature transport measurements to be conducted on mackinawite. The sample shows semiconducting-like behaviour up to the maximum pressures applied but with a gradual flattening of the resistivity curve it is tentatively suggested that the system will undergo a semiconductor–metallic transition with a further application of pressure. Interestingly, this contradicts band structure and more recent density functional theory (DFT) calculations which predict a metallic system. However, the experimental data agrees with the original prediction of semiconducting behaviour made by Bertaut 1965. This research also shows that, at least in its parent form, mackinawite does not exhibit a superconductive state unlike its iso-structural counterpart tetragonal FeSe. This is also briefly discussed.

Superconductivity in polycrystalline Fe1+d Te0.9Se0.1 was enhanced by heating in alcoholic beverages. We found that part of the excess Fe was deintercalated from the interlayer sites by the treatment and the shielding volume fractions were increased with the reduction of excess Fe content in sample. This behavior is similar to the case of Fe1+d Te1−x S x . Thus the technique of alcoholic beverage treatment can be applied generally to the Fe-chalcogenide superconductors.

The effects of uniaxial strain and hydrostatic pressure on Hg0.83Re0.18Ba2Ca2.4Cu3.6O14 [Hg0.83(Re0.18)-1223] were investigated by ac magnetic measurements under stress corresponding to a pressure of 20 GPa at maximum. According to a previous thermal study based on the Ehrenfest relation, in-plane contraction should increase the superconducting transition temperature Tc, whereas out-of-plane contraction should decrease Tc. This suggests that the increase in Tc under hydrostatic-pressure contraction must be smaller than that under in-plane contraction. However, the present uniaxial-strain experiments revealed enhancement of Tc under both in-plane and out-of-plane contraction, and the largest enhancement was observed under hydrostatic-pressure contraction. According to a band calculation, all contraction styles induce hole doping from the HgO blocks to the CuO2 blocks, and hydrostatic-pressure contraction yields the largest hole doping among three contractions. This behavior explains well a series of changes in Tc in the stress region of below 8 GPa. More specifically, under hydrostatic-pressure contraction, Tc exhibited an increase, a decrease, and another increase with increasing pressure, and this multistep change is similar to that observed in Bi-2223-type cuprate superconductors, suggesting that it is necessary to distinguish the effect of strain on the middle CuO2 plane in the three-CuO2-plane package from that on the outer planes.

K$_x$Fe$_{2-y}$Se$_2$ exhibits an iron-vacancy ordering at $T_{\rm s} {\sim}270{\deg}$C and separates into two phases: a minor superconducting (iron-vacancy-disordered) phase and a major non-superconducting (iron-vacancy-ordered) phase. The microstructural and superconducting properties of this intermixture can be tuned by an appropriate control of the quenching process through $T_{\rm s}$. A faster quenching rate leads to a finer microstructure and a suppression of formation of the non-superconducting phase by up to 50%. Nevertheless, such a faster cooling rate does induce a monotonic reduction in the superconducting transition temperature (from 30.7 K down to 26.0 K) and, simultaneously, a decrease in the iron content within the superconducting phase such that the compositional ratio changed from K$_{0.35}$Fe$_{1.83}$Se$_2$ to K$_{0.58}$Fe$_{1.71}$Se$_2$.

Superconducting single crystals of Rb-intercalated FeSe compounds Rb$_x$Fe$_{2-y}$Se$_2$ were prepared by using a starting material of Rb$_2$Se as a Rb source. The superconducting properties and the surface microstructures were systematically controlled by varying the cooling rate in the quenching process. The higher cooling rate in the sample provided a higher superconducting transition temperature with highly connected superconducting mesh-like surface structure. Extremely slow-cooling process led to the complete isolation between the superconducting domains., Comment: 15 pages, 6 figures

Potassium intercalated FeSe has been reported as a superconductor with superconducting transition temperatures ($T_{\rm c}$'s) of 30-48 K. However, there is no clear answer to identify the relationship between the surface morphology, compositional ratio and its crystal structure. This report directly reveals the correspondence among these three characteristics in single crystals with a $T_{\rm c}$ onset of around 44 K using a micro-sampling technique. Island-like parts on the surface of the crystals clearly have the K$_x$Fe$_2$Se$_2$ structure with perfect FeSe layers, which is formed in conjunction with the K$_2$Fe$_4$Se$_5$ phase. This results in the appearance of the $T_{\rm c}$ onset of 44 K., 15 pages, 6 figures

A novel diamond anvil cell suitable for electrical transport measurements under high pressure has been developed. A boron-doped metallic diamond film was deposited as an electrode on a nano-polycrystalline diamond anvil using a microwave plasma-assisted chemical vapor deposition technique combined with electron beam lithography. The maximum pressure that can be achieved by this assembly is above 30 GPa. We report electrical transport measurements of Pb up to 8 GPa. The boron-doped metallic diamond electrodes showed no signs of degradation after repeated compression.

Phase diagrams of as-grown and O 2 -annealed FeTe 1− x Se x determined from magnetic susceptibility measurement were obtained. For as-grown samples, the antiferromagnetic order was fully suppressed in the range region x ≥0.15, and weak superconductivity appeared when x ≥0.1. Beginning at x =0.5, weak superconductivity was found to evolve into bulk superconductivity. Interestingly, for O 2 -annealed samples, complete suppression of magnetic order and the occurrence of bulk superconductivity were observed when x ≥0.1. We found that O 2 -annealing induces bulk superconductivity for FeTe 1− x Se x . Oxygen probably plays a key role in the suppression of the magnetic order and the appearance of bulk superconductivity.

We have performed scanning tunneling microscopy on Fe1.07Te that is the parent compound of the iron-chalcogenide superconductors (SCs). The results indicate the existence of the unidirectional electronic order with a period of a 0 (a 0 interchalcogen distance) along one Te–Te direction. From the one-dimensionality of the electronic order, it is believed that the structural or antiferromagnetic transition is closely related to the formation of this electronic order. The results in this study will be crucial key in understanding the parent state of iron-chalcogenide SCs.

We have tried self-flux and pulsed laser deposition (PLD) method to make single crystals of RuSr2GdCu2O8. In the self-flux method, we added the excess optimum solvent (Ru:Gd:Cu = 0.8:0.4:1.7) during growth under a low cooling rate of 1.5iC/hr. But, we could not find any single crystals. In the PLD method, we found the growth condition of single crystal phase with substrate temperature (∼800 °C) and substrates (SrTiO3).

Based on extensive Mossbauer effect (ME) and magnetization measurements, the orthorhombic AlFe2B2 was characterized as a ferromagnet (FM) because this character is evident as an onset of a FM transition at Tc=320 K and characteristic magnetizations isotherms below Tc. At liquid helium temperatures, the magnetization saturates to μ sat ≈ 1 μ B per Fe atom; a value which is half the one reported for the iron metal indicating a relatively more filled 3d band. The ME analysis revealed a hyperfine field H(0) of 88(2) kOe, an isomer shift (relative to Fe) of 0.50(2) mm/s, and a quadrupole parameter of 0.02 mm/s: all parameters extrapolated to zero Kelvin. The itinerant character of the magnetic moment will be discussed.

Isoelectronic Tellurium (Te) substitution for Selenium (Se) in the tetragonal phase of FeSe (β-FeSe) increases the superconducting transition temperature ( T c ) by applying a negative pressure on the lattice. However, the normal state resistivity increases and shows semi-metallic behavior for samples with higher Te concentration. With increasing Te concentration, the T c increases and reaches a maximum for FeSe 0.5 Te 0.5 and then decreases with further increase of Te. We have investigated the effect of Cobalt (Co) and Nickel (Ni) doping in FeSe 0.5 Te 0.5 in the nominal composition range Fe 1− x TM x Se 0.5 Te 0.5 (TM = Co ( x = 0.05, 0.1, 0.15, 0.2) and Ni ( x = 0.05, 0.1)). Both Co and Ni doping suppress T c and drives the system to metal–insulator transition. The in-plane (‘ a ’) and out-of-plane (‘ c ’) lattice constants decrease with increasing dopant concentration.